1. Field of the Invention
The present invention relates to an energy harvesting device for converting kinetic energy caused by external vibration into electric energy and, more particularly, to a technology of maximizing energy harvesting efficiency by means of an energy harvesting device having a structure such that an inherent vibration frequency thereof coincides with an external vibration frequency so as to generate resonance.
2. Description of the Related Art
Recently, a remarkable growth of industries related to energy saving and renewable energy is being accelerated. Accordingly, research on energy saving and utilization of new energy harvesting sources through harvest of consumed energy and conversion of the harvested energy into usable energy such as electric power, etc. is being conducted.
Especially, research on an energy harvesting device for generating power by harvesting kinetic energy caused by external motion is also being widely conducted. Representative energy harvesting devices include the following technologies: (1) including a piezoelectric element and converting kinetic energy generated when an element having a predetermined mass moves by external vibration into electric energy through a piezoelectric effect of the piezoelectric element, or (2) converting induced electromotive force generated by electromagnetic induction by movement of an element into electric energy.
A conventional energy harvesting device includes a cantilever-type vibration body having a fixed end and a free end capable of free motion, and a piezoelectric element or a magnet-coil structure mounted to the free end. Such a conventional energy harvesting device harvests energy by charging a power storage unit with electricity generated by piezoelectric effect or electromagnetic induction as the vibration body vibrates.
The vibration body of the energy harvesting device has an inherent vibration frequency according to vibration characteristics. When the external vibration frequency and the inherent vibration frequency of the vibration body of the energy harvesting device coincide and thus resonance is generated, energy harvesting efficiency may be maximized.
However, because the inherent vibration frequency of the vibration body is set when manufacturing the conventional energy harvesting device, in order to generate resonance corresponding to the external vibration frequency which varies depending on the mounting position, the inherent vibration frequency should be adjusted when producing the energy harvesting device. Further, at present, because there is no technology capable of changing the inherent vibration frequency of the vibration body to generate resonance when the external vibration frequency varies, energy harvesting efficiency is deteriorated.